// Copyright 2014 the V8 project authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef V8_BASE_BITS_H_
#define V8_BASE_BITS_H_

#include <stdint.h>
#include <type_traits>

#include "src/base/base-export.h"
#include "src/base/macros.h"
#if V8_CC_MSVC
#include <intrin.h>
#endif
#if V8_OS_WIN32
#include "src/base/win32-headers.h"
#endif

namespace v8 {
namespace base {
    namespace bits {

        // CountPopulation(value) returns the number of bits set in |value|.
        template <typename T>
        constexpr inline
            typename std::enable_if<std::is_unsigned<T>::value && sizeof(T) <= 8,
                unsigned>::type
            CountPopulation(T value)
        {
#if V8_HAS_BUILTIN_POPCOUNT
            return sizeof(T) == 8 ? __builtin_popcountll(static_cast<uint64_t>(value))
                                  : __builtin_popcount(static_cast<uint32_t>(value));
#else
            constexpr uint64_t mask[] = { 0x5555555555555555, 0x3333333333333333,
                0x0f0f0f0f0f0f0f0f, 0x00ff00ff00ff00ff,
                0x0000ffff0000ffff, 0x00000000ffffffff };
            value = ((value >> 1) & mask[0]) + (value & mask[0]);
            value = ((value >> 2) & mask[1]) + (value & mask[1]);
            value = ((value >> 4) & mask[2]) + (value & mask[2]);
            if (sizeof(T) > 1)
                value = ((value >> (sizeof(T) > 1 ? 8 : 0)) & mask[3]) + (value & mask[3]);
            if (sizeof(T) > 2)
                value = ((value >> (sizeof(T) > 2 ? 16 : 0)) & mask[4]) + (value & mask[4]);
            if (sizeof(T) > 4)
                value = ((value >> (sizeof(T) > 4 ? 32 : 0)) & mask[5]) + (value & mask[5]);
            return static_cast<unsigned>(value);
#endif
        }

        // ReverseBits(value) returns |value| in reverse bit order.
        template <typename T>
        T ReverseBits(T value)
        {
            DCHECK((sizeof(value) == 1) || (sizeof(value) == 2) || (sizeof(value) == 4) || (sizeof(value) == 8));
            T result = 0;
            for (unsigned i = 0; i < (sizeof(value) * 8); i++) {
                result = (result << 1) | (value & 1);
                value >>= 1;
            }
            return result;
        }

        // CountLeadingZeros(value) returns the number of zero bits following the most
        // significant 1 bit in |value| if |value| is non-zero, otherwise it returns
        // {sizeof(T) * 8}.
        template <typename T, unsigned bits = sizeof(T) * 8>
        inline constexpr
            typename std::enable_if<std::is_unsigned<T>::value && sizeof(T) <= 8,
                unsigned>::type
            CountLeadingZeros(T value)
        {
            static_assert(bits > 0, "invalid instantiation");
#if V8_HAS_BUILTIN_CLZ
            return value == 0
                ? bits
                : bits == 64
                    ? __builtin_clzll(static_cast<uint64_t>(value))
                    : __builtin_clz(static_cast<uint32_t>(value)) - (32 - bits);
#else
            // Binary search algorithm taken from "Hacker's Delight" (by Henry S. Warren,
            // Jr.), figures 5-11 and 5-12.
            if (bits == 1)
                return static_cast<unsigned>(value) ^ 1;
            T upper_half = value >> (bits / 2);
            T next_value = upper_half != 0 ? upper_half : value;
            unsigned add = upper_half != 0 ? 0 : bits / 2;
            constexpr unsigned next_bits = bits == 1 ? 1 : bits / 2;
            return CountLeadingZeros<T, next_bits>(next_value) + add;
#endif
        }

        inline /*constexpr*/ unsigned CountLeadingZeros32(uint32_t value)
        {
            return CountLeadingZeros(value);
        }
        inline /*constexpr*/ unsigned CountLeadingZeros64(uint64_t value)
        {
            return CountLeadingZeros(value);
        }

        // CountTrailingZeros(value) returns the number of zero bits preceding the
        // least significant 1 bit in |value| if |value| is non-zero, otherwise it
        // returns {sizeof(T) * 8}.
        template <typename T, unsigned bits = sizeof(T) * 8>
        inline constexpr
            typename std::enable_if<std::is_integral<T>::value && sizeof(T) <= 8,
                unsigned>::type
            CountTrailingZeros(T value)
        {
#if V8_HAS_BUILTIN_CTZ
            return value == 0 ? bits
                              : bits == 64 ? __builtin_ctzll(static_cast<uint64_t>(value))
                                           : __builtin_ctz(static_cast<uint32_t>(value));
#else
            // Fall back to popcount (see "Hacker's Delight" by Henry S. Warren, Jr.),
            // chapter 5-4. On x64, since is faster than counting in a loop and faster
            // than doing binary search.
            using U = typename std::make_unsigned<T>::type;
            U u = value;
            return CountPopulation(static_cast<U>(~u & (u - 1u)));
#endif
        }

        inline /*constexpr*/ unsigned CountTrailingZeros32(uint32_t value)
        {
            return CountTrailingZeros(value);
        }
        inline /*constexpr*/ unsigned CountTrailingZeros64(uint64_t value)
        {
            return CountTrailingZeros(value);
        }

        // Returns true iff |value| is a power of 2.
        template <typename T,
            typename = typename std::enable_if<std::is_integral<T>::value || std::is_enum<T>::value>::type>
        constexpr inline bool IsPowerOfTwo(T value)
        {
            return value > 0 && (value & (value - 1)) == 0;
        }

        // RoundUpToPowerOfTwo32(value) returns the smallest power of two which is
        // greater than or equal to |value|. If you pass in a |value| that is already a
        // power of two, it is returned as is. |value| must be less than or equal to
        // 0x80000000u. Uses computation based on leading zeros if we have compiler
        // support for that. Falls back to the implementation from "Hacker's Delight" by
        // Henry S. Warren, Jr., figure 3-3, page 48, where the function is called clp2.
        V8_BASE_EXPORT uint32_t RoundUpToPowerOfTwo32(uint32_t value);
        // Same for 64 bit integers. |value| must be <= 2^63
        V8_BASE_EXPORT uint64_t RoundUpToPowerOfTwo64(uint64_t value);
        // Same for size_t integers.
        inline size_t RoundUpToPowerOfTwo(size_t value)
        {
            if (sizeof(size_t) == sizeof(uint64_t))
                return (size_t)RoundUpToPowerOfTwo64(value);
            else
                return RoundUpToPowerOfTwo32(value);
        }

        // RoundDownToPowerOfTwo32(value) returns the greatest power of two which is
        // less than or equal to |value|. If you pass in a |value| that is already a
        // power of two, it is returned as is.
        inline uint32_t RoundDownToPowerOfTwo32(uint32_t value)
        {
            if (value > 0x80000000u)
                return 0x80000000u;
            uint32_t result = RoundUpToPowerOfTwo32(value);
            if (result > value)
                result >>= 1;
            return result;
        }

        // Precondition: 0 <= shift < 32
        inline uint32_t RotateRight32(uint32_t value, uint32_t shift)
        {
            if (shift == 0)
                return value;
            return (value >> shift) | (value << (32 - shift));
        }

        // Precondition: 0 <= shift < 32
        inline uint32_t RotateLeft32(uint32_t value, uint32_t shift)
        {
            if (shift == 0)
                return value;
            return (value << shift) | (value >> (32 - shift));
        }

        // Precondition: 0 <= shift < 64
        inline uint64_t RotateRight64(uint64_t value, uint64_t shift)
        {
            if (shift == 0)
                return value;
            return (value >> shift) | (value << (64 - shift));
        }

        // Precondition: 0 <= shift < 64
        inline uint64_t RotateLeft64(uint64_t value, uint64_t shift)
        {
            if (shift == 0)
                return value;
            return (value << shift) | (value >> (64 - shift));
        }

        // SignedAddOverflow32(lhs,rhs,val) performs a signed summation of |lhs| and
        // |rhs| and stores the result into the variable pointed to by |val| and
        // returns true if the signed summation resulted in an overflow.
        inline bool SignedAddOverflow32(int32_t lhs, int32_t rhs, int32_t* val)
        {
#if V8_HAS_BUILTIN_SADD_OVERFLOW
            return __builtin_sadd_overflow(lhs, rhs, val);
#else
            uint32_t res = static_cast<uint32_t>(lhs) + static_cast<uint32_t>(rhs);
            *val = bit_cast<int32_t>(res);
            return ((res ^ lhs) & (res ^ rhs) & (1U << 31)) != 0;
#endif
        }

        // SignedSubOverflow32(lhs,rhs,val) performs a signed subtraction of |lhs| and
        // |rhs| and stores the result into the variable pointed to by |val| and
        // returns true if the signed subtraction resulted in an overflow.
        inline bool SignedSubOverflow32(int32_t lhs, int32_t rhs, int32_t* val)
        {
#if V8_HAS_BUILTIN_SSUB_OVERFLOW
            return __builtin_ssub_overflow(lhs, rhs, val);
#else
            uint32_t res = static_cast<uint32_t>(lhs) - static_cast<uint32_t>(rhs);
            *val = bit_cast<int32_t>(res);
            return ((res ^ lhs) & (res ^ ~rhs) & (1U << 31)) != 0;
#endif
        }

        // SignedMulOverflow32(lhs,rhs,val) performs a signed multiplication of |lhs|
        // and |rhs| and stores the result into the variable pointed to by |val| and
        // returns true if the signed multiplication resulted in an overflow.
        V8_BASE_EXPORT bool SignedMulOverflow32(int32_t lhs, int32_t rhs, int32_t* val);

        // SignedAddOverflow64(lhs,rhs,val) performs a signed summation of |lhs| and
        // |rhs| and stores the result into the variable pointed to by |val| and
        // returns true if the signed summation resulted in an overflow.
        inline bool SignedAddOverflow64(int64_t lhs, int64_t rhs, int64_t* val)
        {
            uint64_t res = static_cast<uint64_t>(lhs) + static_cast<uint64_t>(rhs);
            *val = bit_cast<int64_t>(res);
            return ((res ^ lhs) & (res ^ rhs) & (1ULL << 63)) != 0;
        }

        // SignedSubOverflow64(lhs,rhs,val) performs a signed subtraction of |lhs| and
        // |rhs| and stores the result into the variable pointed to by |val| and
        // returns true if the signed subtraction resulted in an overflow.
        inline bool SignedSubOverflow64(int64_t lhs, int64_t rhs, int64_t* val)
        {
            uint64_t res = static_cast<uint64_t>(lhs) - static_cast<uint64_t>(rhs);
            *val = bit_cast<int64_t>(res);
            return ((res ^ lhs) & (res ^ ~rhs) & (1ULL << 63)) != 0;
        }

        // SignedMulHigh32(lhs, rhs) multiplies two signed 32-bit values |lhs| and
        // |rhs|, extracts the most significant 32 bits of the result, and returns
        // those.
        V8_BASE_EXPORT int32_t SignedMulHigh32(int32_t lhs, int32_t rhs);

        // SignedMulHighAndAdd32(lhs, rhs, acc) multiplies two signed 32-bit values
        // |lhs| and |rhs|, extracts the most significant 32 bits of the result, and
        // adds the accumulate value |acc|.
        V8_BASE_EXPORT int32_t SignedMulHighAndAdd32(int32_t lhs, int32_t rhs,
            int32_t acc);

        // SignedDiv32(lhs, rhs) divides |lhs| by |rhs| and returns the quotient
        // truncated to int32. If |rhs| is zero, then zero is returned. If |lhs|
        // is minint and |rhs| is -1, it returns minint.
        V8_BASE_EXPORT int32_t SignedDiv32(int32_t lhs, int32_t rhs);

        // SignedMod32(lhs, rhs) divides |lhs| by |rhs| and returns the remainder
        // truncated to int32. If either |rhs| is zero or |lhs| is minint and |rhs|
        // is -1, it returns zero.
        V8_BASE_EXPORT int32_t SignedMod32(int32_t lhs, int32_t rhs);

        // UnsignedAddOverflow32(lhs,rhs,val) performs an unsigned summation of |lhs|
        // and |rhs| and stores the result into the variable pointed to by |val| and
        // returns true if the unsigned summation resulted in an overflow.
        inline bool UnsignedAddOverflow32(uint32_t lhs, uint32_t rhs, uint32_t* val)
        {
#if V8_HAS_BUILTIN_SADD_OVERFLOW
            return __builtin_uadd_overflow(lhs, rhs, val);
#else
            *val = lhs + rhs;
            return *val < (lhs | rhs);
#endif
        }

        // UnsignedDiv32(lhs, rhs) divides |lhs| by |rhs| and returns the quotient
        // truncated to uint32. If |rhs| is zero, then zero is returned.
        inline uint32_t UnsignedDiv32(uint32_t lhs, uint32_t rhs)
        {
            return rhs ? lhs / rhs : 0u;
        }

        // UnsignedMod32(lhs, rhs) divides |lhs| by |rhs| and returns the remainder
        // truncated to uint32. If |rhs| is zero, then zero is returned.
        inline uint32_t UnsignedMod32(uint32_t lhs, uint32_t rhs)
        {
            return rhs ? lhs % rhs : 0u;
        }

        // SignedSaturatedAdd64(lhs, rhs) adds |lhs| and |rhs|,
        // checks and returns the result.
        V8_BASE_EXPORT int64_t SignedSaturatedAdd64(int64_t lhs, int64_t rhs);

        // SignedSaturatedSub64(lhs, rhs) subtracts |lhs| by |rhs|,
        // checks and returns the result.
        V8_BASE_EXPORT int64_t SignedSaturatedSub64(int64_t lhs, int64_t rhs);

    } // namespace bits
} // namespace base
} // namespace v8

#endif // V8_BASE_BITS_H_
